1. Technical Field
The invention relates to an image forming method for use in an electrophotographic copying machine or printer.
2. Related Art
In recent years, as a result of the modern progress of digital image processing techniques, digital image formation has become a mainstream of image forming methods. In the digital image forming method, basically, images comprised of minute dots of, for example, 400 dpi (dots per inch; the number of dots per 2.54 cm) are developed. Thus, high image quality techniques capable of faithfully reproducing such minute dot images are needed. Especially, in recent years, demands for compactness, higher resolution and full color image formation of copying machines and for improved resolution of printers have increased. In case higher accuracy such as high resolution is needed, further improved image quality techniques are also demanded.
With a view toward realization of such high image quality, studies have been made on reduction of the particle diameter of toner while controlling the shape factors and the particle size distribution thereof. In particular, an attempt has been made to reduce the toner particle diameter while narrowing shape distribution and particle size distribution of the toner for the purpose of realizing improved resolution and precise reproduction of fine half tone images, thereby realizing an improved image quality. However, the intended high quality images are not obtainable in practice by using small diameter toner. Rather, some problems result from the use of small diameter toner. A problem in cleaning is one of them. Since the apparent adhesive force of such small toner onto a photoreceptor increases, it is difficult to clean the photoreceptor. In particular, since the toner obtained by emulsion polymerization method or suspension polymerization method effective to prepare small diameter toner has not only a small particle diameter but also a high particle roundness. Therefore, in the cleaning-process for cleaning the photoreceptor with a cleaning blade, toner particles remaining on the photoreceptor have a tendency to pass through between the photoreceptor and the edge of the cleaning blade to cause cleaning failure.
In order to solve the above problems, it is important that processing units constituting an electrophotographic image forming apparatus should have high accuracy. Especially, it is required that the positional relationship between the surface of a photoreceptor and each of a developing section, a transfer section and a cleaner should be strictly maintained. Displacement from the original relationship of those positions is apt to causes the following image defects:
(1) A positional displacement between the photoreceptor and the exposing section causes a reduction of resolution due to a focal offset of a laser beam;
(2) A positional displacement between the photoreceptor and the developing section (Dsd) causes fogs, a reduction of the image density and a reduction of resolution;
(3) A positional displacement between the photoreceptor and the transfer section causes a reduction of the image quality such as thin spots and blurs of the transferred image; and
(4) A positional displacement between the photoreceptor and the cleaning blade involves a variation of the blade pressure, causing a cleaning failure and reduction of durability of the photoreceptor.
As described above, it will be understood that the above positional displacement between the photoreceptor and the image forming members around the photoreceptor significantly adversely affects the image quality of the electrophotographic image and also one of the factors for defining such positional relationship is positional accuracy of the photoreceptor.